A drug is a chemical substance, natural or synthetic, which has an action on body metabolism. This action may be helpful or harmful. Pharmacology is the study of the action of drugs on the animal organism and medicinal therapeutics is the science and art of using the action of drugs in the treatment of disease. Until this century, the number of drugs known to man, with a potent therapeutic action, was limited, but during this century, many powerful drugs have been discovered to aid in the control of disease. Readers will be aware of the antibiotics which help to control infection. Nowadays, some diseases of the endocrine glands (glands of internal secretion, such as the thyroid gland and pituitary gland) can be controlled by medication; for example, the young diabetic can now live a relatively normal life, provided he has a daily injection of insulin. Many epileptics (people who suffer from recurring episodes in which they may lose consciousness-see Chapter 16) are able to lead satisfying lives ifthey take drugs to control their attacks; these drugs, known as anticonvulstants, have to be taken regularly over a long period. For reasons like this, there is a small group of teenagers for whom drug-taking is beneficial and may, indeed, be essential for life and health. (It is an unfortunate sign of the times to report that epileptics have occasionally been, mistakenly, regarded as misusing drugs and attempts have been made to wean them off
their medically-prescribed anti-convulsant tablets, by well-meaning but misguided adults.)
The effects of appropriately prescribed drugs are largely beneficial but, inevitably, there are undesirable side effects and often the therapeutic dose is very close to the level at which toxic effects may appear. By and large, adolescents are healthy and rarely have to seek medical advice. If an adolescent has a headache or cough, he may consult his local chemist for an appropriate painkiller or cough-mixture, or he may select his own medication from the shelf at the local supermarket without prior consultation. The re-introduction of the National Health Service prescription charge has encouraged self-medication in many groups of people.